The Rutgers hybrid dogwood: naming and genetic diversity analysis

Big-bracted dogwoods (Cornus spp.) are popular landscape trees in the United States, accounting for $30 million in sales annually. This group of dogwoods is comprised of the Florida dogwood (C. florida), the Asian dogwood (C. kousa) and the Pacific dogwood (C. nuttallii). They are beloved for their four season appeal: floral bract display in the spring, attractive green foliage in the summer, striking autumun colors in the fall and exfoliating bark in the winter. These trees are the focus of a big-bracted dogwood breeding program at Rutgers University, which started in the 1960s under the helm of Dr. Elwin Orton. His focus was to develop new pink or red-bracted varieties of C. kousa and red-bracted dwarf varieties of C. florida. In order to accomplish these breeding goals, Dr. Orton created the first inter-specific hybrids between C. florida × C. kousa and C. kousa × C. nuttallii. These hybrids have since become an important staple in the horticultural trade known for their vigor, enhanced disease tolerance and improved ornamental qualities. Part of this study was to formally name and describe these hybrids in order to facilitate scientific and horticultural communication. The C. florida × C. kousa hybrids were formally named Cornus × rutgersensis in honor of Rutgers University and the C. kousa × C. nuttallii were named Cornus × elwinortonii in honor of Dr. Elwin Orton. Only a handful of these hybrids were fertile potentially creating a genetic bottleneck in the Rutgers germplasm collection when they were used in breeding. Big-bracted dogwoods are highly heterozygous and sensitive to inbreeding depression requiring the breeding program to maintain high levels of genetic diversity within its breeding lines. Genetic diversity levels in the Rutgers breeding program are uknown. This study sought to elucidate the level of genetic diversity in 276 Rutgers University dogwood accessions and 59 from the University of Tennessee by using eleven simple sequence repeat molecular markers. Results showed that five consensus groups were found: C. florida group, Cornus × rutgersensis group, Cornus × elwinortonii group, C. kousa inter-specfic hybrid group and Pink-bracted C. kousa group. It was found that genetic diversity is high across the entire germplasm collection tested; however, limited genetic diversity exists within the Cornus × rutgers and Cornus × elwinortonii groups. This information will be important in the future of the Rutgers and other breeding programs allowing breeders to make more genetically distant crosses to help maintain high levels of genetic diversity.M.S.Includes bibliographical referencesby Robert Mattera II